Is carried out the mathematical simulation of heat transfer processes in the small environment of vaporizer camera of heat pump (HP) when the source of low-potential energy is present. Are obtained the temperature distributions, which characterize thermal condition HP. Is carried out the comparative analysis of the results of mathematical simulation and experimental data from the work of heat-pumping installation in the conditions of relatively low (up to 4 °С) temperatures. In the experiments, the partial freezing around of the tubes of vaporizer is established. It is revealed, that the formation of the layer of ice on the surface of vaporizer leads to the temperature contrast by the volume of liquid in the camera and reduction in the effectiveness in the work of heat-pumping installation.